Sodium bismuthate is an inorganic compound, and a strong oxidiser with chemical formula NaBiO₃. It is somewhat hygroscopic, but not soluble in cold water, which can be convenient since the reagent can be easily removed after the reaction. It is one of the few water insoluble sodium salts. Commercial samples may be a mixture of bismuth(V) oxide, sodium carbonate and sodium peroxide.

A related compound with the approximate formula Na₃BiO₄ also exists.

Sodium bismuthate adopts an ilmenite structure, consisting of octahedral bismuth(V) centers and sodium cations. The average Bi–O distance is 2.116 Å. The ilmenite structure is related to the corundum structure (Al₂O₃) with a layer structure formed by close packed oxygen atoms with the two different cations alternating in octahedral sites.

Bismuth oxidizes to the +5 oxidation state only with difficulty in the absence of alkali. Synthesis is performed by making a suspension of bismuth trioxide in a boiling sodium hydroxide solution. It is then oxidized by addition of bromine to form sodium bismuthate.

Another synthesis of NaBiO₃ involves oxidizing a mixture of sodium oxide and bismuth(III) oxide with air (as the source of O₂):

The procedure is analogous to the oxidation of manganese dioxide in alkali to give sodium manganate.

Storage conditions with moisture and high temperatures are detrimental to sodium bismuthate, as it oxidizes water, decomposing into sodium hydroxide and bismuth(III) oxide:

It is decomposed faster by acids. In HCl, NaBiO₃ also reacts to form chlorine gas.